A conventional domestic fan typically includes a set of blades or vanes mounted for rotation about an axis, and drive apparatus for rotating the set of blades to generate an air flow. The movement and circulation of the air flow creates a ‘wind chill’ or breeze and, as a result, the user experiences a cooling effect as heat is dissipated through convection and evaporation. The blades are generally located within a cage which allows an air flow to pass through the housing while preventing users from coming into contact with the rotating blades during use of the fan.
U.S. Pat. No. 2,488,467 describes a fan which does not use caged blades to project air from the fan assembly. Instead, the fan assembly comprises a base which houses a motor-driven impeller for drawing an air flow into the base, and a series of concentric, annular nozzles connected to the base and each comprising an annular outlet located at the front of the nozzle for emitting the air flow from the fan. Each nozzle extends about a bore axis to define a bore about which the nozzle extends.
Each nozzle is in the shape of an airfoil. An airfoil may be considered to have a leading edge located at the rear of the nozzle, a trailing edge located at the front of the nozzle, and a chord line extending between the leading and trailing edges. In U.S. Pat. No. 2,488,467 the chord line of each nozzle is parallel to the bore axis of the nozzles. The air outlet is located on the chord line, and is arranged to emit the air flow in a direction extending away from the nozzle and along the chord line.
Another fan assembly which does not use caged blades to project air from the fan assembly is described in WO 2010/100451. This fan assembly comprises a cylindrical base which also houses a motor-driven impeller for drawing a primary air flow into the base, and a single annular nozzle connected to the base and comprising an annular mouth through which the primary air flow is emitted from the fan. The nozzle defines an opening through which air in the local environment of the fan assembly is drawn by the primary air flow emitted from the mouth, amplifying the primary air flow. The nozzle includes a Coanda surface over which the mouth is arranged to direct the primary air flow. The Coanda surface extends symmetrically about the central axis of the opening so that the air flow generated by the fan assembly is in the form of an annular jet having a cylindrical or frusto-conical profile.
GB 2,479,760 describes a modification of the fan assembly described in WO 2010/100451. The cylindrical base of the fan assembly is increased in height to accommodate an electrostatic filter for removing particulates from the primary air flow before it enters the annular nozzle. The electrostatic filter is connected to an electrical influence machine located in the base of the fan assembly so that power generated by the electrical influence machine is supplied to the electrostatic filter.